The present invention relates to an apparatus for judging a catalyst of a catalytic converter for exhaust gas clarification with respect to deterioration, the catalytic converter being provided in an exhaust system of an internal combustion engine.
An apparatus for detecting deterioration of a catalyst of a catalytic converter provided in an exhaust system of an internal combustion engine is disclosed in the Japanese Patent Provisional Publication No. 61-286550, the technique of which involves comparing a predetermined threshold for judgment of catalyst deterioration with the output signal of an O.sub.2 sensor provided at a downstream side of the catalytic converter. There is a problem which arises with such an apparatus, however, in that, because of the detection based upon the comparison of the output signal with the threshold fixed, the detection of the catalyst deterioration can be accompany of detection errors irrespective of the catalyst itself being still usable at that time if the O.sub.2 sensor itself is deteriorated. In other words, since the output signal of the O.sub.2 sensor is compared with the predetermined threshold, which is constant and fixed, for the catalyst deterioration detection purpose, difficulty is encountered to adequately judge between the deterioration of the catalyst and the deterioration of the O.sub.2 sensor.